1. Field of the Invention
This invention relates to a focus state detecting device in a camera or the like, and in particular to a focus state detecting device in which the pupil of the imaging lens of a camera is divided into a plurality of areas, a plurality of secondary object images are formed by light beams passed through said areas and the focus position of the imaging lens is detected from the relative positional relation between these secondary object images.
2. Description of the Prior Art
A conventional device of this type is disclosed in Japanese Laid-open Patent Application No. 95221/1977.
In such focus detecting device, in order to prevent light beams other than a focus detecting light beam, i.e., stray light, from entering photoelectric converting means to cause an error of measured distance, a field mask is provided on or near a primary imaging plane. The size and location of this field mask must be limited so that a plurality of images of the field mask formed by a re-imaging system do not overlap one another on the photoelectric converting means. Therefore, if an attempt is made to apply such focus detecting device to a single lens reflex camera, there is the disadvantage that the location of the focus detecting device is limited to the bottom of the camera or the entire device becomes bulky.